I have been trying out the v3 alpha (Mac OS X, #26) and am found some quirks/bugs. Some need more testing before I am sure what is going on. Do you want them here or in the wiki?
e.g. I am pretty sure this is a bug
Yeah, that's a bug. I can't reproduce it so it must be one of the bugs that I fixed already. I'll put out a new alpha release with the latest bug fixes and feature updates.
ETA - I just noticed that your loop body contains path operations and a path command. This wasn't allowed in version 2, but is allowed in version 3. I just didn't implement it correctly.
Yes, the bug only occurs if you have a loop that has both path operations (MOVETO, LINETO, etc) and path commands (STROKE and FILL). Loops in rules are OK, as are loops in paths that don't mix operations and commands.